Rubidium Atomic Frequency Standards
FEI's Legacy Rubidium Product
Model FE-5600M

Fast warm-up
MIL-E-5400 Class II
Lightweight, small, rugged
Raw aircraft power operation
Modular construction

Function Description   Technical Characteristics

The RFS uses the property of atomic resonance in a Rubidium Physics Package to control the output frequency of a 50.255+ MHz Voltage Controlled Crystal Oscillator (VCXO) via a Frequency Lock Loop (FLL). The FLL functional blocks consist of an RF Generator, Lock-in Amplifier and the Rubidium Physics Package. Frequency locking of the VCXO is accomplished by operating the Rubidium Physics Package as a frequency discriminator, i.e., departures of a frequency derived from an input signal (50.255+ MHz from the VCXO) from a defined center frequency (Rubidium atomic resonance) produce a DC output signal (control voltage). Once the FLL has been established, the system generates a loop-locked indication which can be monitored on pin 3. Depending on the option selected, the 50.255+ MHz VCXO output is used as the clock input for the DDS within the Synthesizer, the Digital Programmable Synthesizer or Buffer Amplifier.

The Rubidium Physics Package utilizes the ground-state hyperfine transition of the Rubidium atom, at approximately 6.8+ GHz. In order to use this atomic transition, the Rubidium Physics Package incorporates a Rubidium cell, Rubidium lamp, and servo electronics. The VCXO is locked to the Rubidium atomic resonance at 6.8+ GHz. The VCXO frequency of 50.255+ MHz is an exact sub-multiple (x136) of the atomic resonance frequency at 6.8+ GHz.

The error signal is generated in the physics package. Light from the Rubidium lamp, produced by an excited plasma discharge, is filtered and passed through the Rubidium resonance cell where it interacts with Rubidium atoms in the vapor. After passing through the resonance cell, this light is incident upon a photocell. When the applied microwave frequency is equal to 6.8+ GHz, the Rubidium atoms are resonated by the microwave field in the cavity; this causes the light reaching the photocell to decrease. The decrease in light, when the microwave frequency is equal to the sharply defined Rubidium frequency, is then converted electronically to an error signal with phase and amplitude information that is used to steer the VCXO via its control voltage and keep it on frequency at 50.255+ MHz.

The input frequency is provided from a digitally Programmable Synthesizer.

Electrical @ 25°C
(unless otherwise specified)
Frequency 10 MHz
Settability (frequency) +/-1 x 10-11
Adjustmant Range 3 x 10-9
Long Term Stability 4 x 10-11/month
2 x 10-10/year
Short Term Stability Averaging Time (SEC) f/f
100 1.4 x 10-11
101 4.4 x 10-12
102 1.4 x 10-12
Warm-up Time <4 min. to
5 x 10-10 @ 25°C
<10 min. to
5 x 10-10 @ -55°C
Retrace 1 x 10-11 when measured at the same temperature, power off <24 hrs.
Output Voltage 0.5 VRMS into 50 ohms
Harmonic Distortion -30dB
Non-Harmonically Related Output -60dB
SSB Phase Noise Offset from Signal
Phase Noise (1 Hz BW)
Hz dBc
101 89
102 125
103 145
Voltage Variation <1 x 10-11 for input voltage range
Power Consumption 25C -55C
During Warm-Up 45 watts max 45 watts max
After Warm-Up 15 watts max 20 watts max
Voltage Required MIL-STD-704, 22 TO 32 Vdc
Size 3.25" x 3.25" x 4.5"
Weight <2.5 pounds
Operational MIL-STD-810, Method 516.2, Proc. 1
Operating -55C to +71C baseplate frequency change < 3 x 10-10
Non-Operating -62C to +95C
Humidity MIL-STD-810, Method 507.1, Proc. 1
Temperature Shock MIL-E-5400, Class II except 71C baseplate 0-40F and Class I curve A>40,000 ft.
Magnetic Field 2 x 10-11 per Gauss (worst case orientation)
Pressure 1 x 10-13/m bar
Acceleration <2 x 10-9/g
Vibration Random-MIL-STD-810 Method 514.2 (5 g rms) Sine - MIL-STD-810 Method 514.2,Proc. VIII (Curve W)
Shock Bench MIL-STD-810, Method 516.2, Half sinewave 20g peak, 11 millisec duration